Combustors are commonly used in industrial and power generation operations to ignite fuel to produce combustion gases having a high temperature and pressure. For example, turbo-machines such as gas turbines typically include one or more combustors to generate power or thrust. A typical gas turbine used to generate electrical power includes an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air may be supplied to the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the working fluid (air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through one or more nozzles into a combustion chamber in each combustor where the compressed working fluid mixes with fuel and ignites to generate combustion gases having a high temperature and pressure. The combustion gases expand in the turbine to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
Various design and operating parameters influence the design and operation of combustors. For example, higher combustion gas temperatures generally improve the thermodynamic efficiency of the combustor. However, higher combustion gas temperatures also promote flashback or flame holding conditions in which the combustion flame migrates towards the fuel being supplied by the nozzles, possibly causing severe damage to the nozzles in a relatively short amount of time. In addition, higher combustion gas temperatures generally increase the disassociation rate of diatomic nitrogen, increasing the production of nitrogen oxides (NOx). Conversely, a lower combustion gas temperature associated with reduced fuel flow and/or part load operation (turndown) generally reduces the chemical reaction rates of the combustion gases, increasing the production of carbon monoxide and unburned hydrocarbons.
In a particular combustor design, the combustor may include an end cap that radially extends across at least a portion of the combustor, and a plurality of tubes may be radially arranged in one or more tube bundles across the end cap to provide fluid communication for the working fluid through the end cap and into the combustion chamber. Fuel may be supplied to a fuel plenum inside the end cap to flow around the tubes and provide convective cooling to the tubes. The fuel may then flow into the tubes and mix with the working fluid flowing through the tubes before flowing out of the tubes and into the combustion chamber.
Although effective at enabling higher operating temperatures while protecting against flashback or flame holding and controlling undesirable emissions, the fuel flowing around and into the tubes may not be evenly distributed. Specifically, the tubes themselves may block the fuel flow and prevent the fuel from evenly flowing over the side of the tube opposite from the direction of the fuel flow. As a result, the convective cooling provided by the fuel and the fuel concentration flowing through the premixer tubes may vary radially across the tube bundle. Both effects may create localized hot spots and/or fuel streaks in the combustion chamber that reduce the design margins associated with flashback or flame holding and may increase undesirable emissions. Therefore, a combustor and method for distributing fuel in the combustor that improves the fuel distribution and cooling would be useful.